Timing control device

ABSTRACT

A timing control device which is suitable for use in controlling equipment in a photographic dark room, includes a pair of electronic switches for alternatively activating either of two loads. A timer is provided which utilizes a wire wound potentiometer for setting a precise timing period. The timing circuit, which includes a resistive-capacitive charging circuit, is utilized to generate a ramp voltage which is fed to the anode of a programmable unijunction transistor, the output of the timing control potentiometer being fed to the gate of this transistor to set the program therefor. The programmable unijunction transistor is utilized to provide a keying signal which actuates an electronic switch which in turn controls the switching circuits associated with the loads. Initiation of the timing action is controlled by means of a touch plate which actuates a switching circuit which in turn activates the timing circuit.

nited States Patent Weinberg [111 3,814,949 1451 June 4,1974

TIMING CONTROL DEVICE Inventor: Stanley Weinberg, 3009 Danalda,

Los Angeles, Calif. 90066 Filed: Sept. 18, 1972 Appl. No.: 289,789

U.S Cl n ..307/l41, 317/141 R Int. Cl. H0111 7/00 Field of Search307/141 R, 141.4; 315/360,

References Cited UNITED STATES PATENTS 2.434.157 1/1948 Heppcard 315/3603,333,175 7/1967 Klyce 307/141 3,671,817. 6/1972 Seipp 307/141 PrimaryExaminer-David Smith, Jr. Attorney, Agent, or FirmEdward A. Sokolski[.57] ABSTRACT A timing control device which is suitable for use incontrolling equipment in a photographic dark room,

includes a pair of electronic switches for alternatively activatingeither of two loads. A timer is provided which utilizes a wire woundpotentiometer for setting a precise timing period. The timing circuit,which includes a resistive-capacitive charging circuit, is utilized togenerate a ramp voltage which is fed to the anode of a programmableunijunction transistor, the output of the timing control potentiometerbeing fed to the gate of this transistor to set the program there- 1for. The programmable unijunction transistor is utilized to provide akeying signal which actuates an electronic switch which in turn controlsthe switching circuits associated with the loads. Initiation of thetiming action is controlled by means of a touch plate which'actuates aswitching circuit which in turn activates the timing circuit.

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FROM POWER CONTROL cmcurr I TIMING CONTROL DEVICE This invention relatesto an electronic timing control device and more particularly to such adevice suitable for controlling the operation of photographic dark roomequipment.

In operating photographic dark room equipment, precise automatic timingof the exposure time of photographic papers is generally required. It isoften desirable to simultaneously control the operation of the dark roomsafe light, i.e. to turn the safe light on whenever the enlargedexposure lamp is off and vice versa. Such'timing control is generallyachieved by means of 'a resistive-capacitive timing circuit utilizing asingle capacitor and a plurality of fixed resistors which areselectively placed in the charging circuit by means of a multipositionselector switch. To obtain precision tim-- ing as is required by theexpert photographer, precision resistors must be utilized which maintaintheir accuracy over long periods of use and under varying temperatureconditions. Also toassure relability, a relatively good quality switchmust be utilized. Such components are generally more costly than wouldbe desired. Further, accuracy of operation, particularly under varyingtemperature conditions, is difficult to maintain as is repeatability ofthe timing operation of units produced on a production line basis.Further, the switch contacts often present reliability problems.

The device of this invention provides an improvement over prior artdevices of the aforementioned type in eliminating the use of variousresistors for selection in the timing circuit and thus the need for aselector switch for selecting such resistors. Rather, a singlewire-wound potentiometer is utilized for selecting the v timing over acontinuous range. This potentiometer is not utilized in theresistive-capacitive charging circuit but rather is used to program aprogrammable unijunction transistor. This eliminates the need for aplurality of high-cost precision resistors as well as a selector switch,and thus cuts the cost of the device and improves its reliability. Thedevice of this inventionadditionally includes a unique touch control forinitiating the timing action with the touching of a touch plate by theoperator without the need for actuating a mechanical switch. Further,stable and reliable electronic switching circuitry is utilized which canbe fabricated with a minimal number of economical components whichaffords accurate and reliable operation.

It is therefore an object of this invention to provide an improvedtiming control device suitable for utilization in controllingphotographic dark room equipment;

It is another object of this invention to provide a timing controldevice of more economical construction than similar prior art devices;

It is still another object of this invention to provide timing controlhaving higher reliability than similar prior art devices;

it is stilla further object of this invention to facilitate the timingcontrol of photographic dark room equipment;

Other objects of this invention become apparent as the descriptionproceeds in connection with the accompanying drawings of which:

F IG. 1 is a functional block diagram illustrating a preferredembodiment of the invention.

FIG. 2 is a functional block diagram of one embodiment of the powercontrol circuit of the preferred embodiment, and

FIG. 3 is a schematic drawing illustrating one embodiment of the timerof the preferred embodiment.

' Briefly described, the device. of the invention is as follows:

A pair of electronic switches are provided to alternatively energizeeither of two loads which may comprise the exposure lamp of aphotographic enlarger and a dark room safe light. Where one of the loadsis a dark room safe light, the switch which controls this light isnormally activated to keep this light on and the enlarger exposure lampoff. A timer is utilized which has a circuit including a programmableunijunction transistor. The programming gate of this transistor iscontrolled with a precision potentiometer by means of which the voltagefed to this gate can be set to a predesired value. 'A'resistive-capacitive charging circuit is utilized to generate a rampvoltage which is fed to the anode of the programmable unijunctiontransistor. The timing action of the timer is initiated by the operatorstouching of a touch plate to operate a series of electronic switches;these switches both initiating the timing operation of the timer andactivating the electronic switch for the enlarger exposure lamp. Whenthe timing period has been completed, i.e. when the ramp voltage at theanode of the programmable unijunction transistor reaches the voltage.set on the timing potentiometer, the transistor provides a keying outputsignal. This signal is used to actuate the aforementioned electronicswitches to cause the switch for the enlarger exposure lamp to bedeactivated and that for the safe light to be activated restoring thedevice to its original condition and placing it in a state for a newtiming cycle.

Referring now to FIG. 1, a functional block diagram of a preferredembodiment of the invention is shown. AC power source 11 is connected bymeans of main power switch 12 across series connected electronicv switch13 and load No. 1,15 and series connected electronic switch 17 and loadNo. 2,19. Electronic switches Band 17 may comprise Triacs. Where theequipment is used to control photographic dark room equipment, load No.1, 15 may comprise the exposure lamp of a photographic enlarger whileload No. 2, 19 may comprise a dark room safe light. During theequipments timing cycle, which is to be explained further on in thespecification, Triac 19 is normally activated to provide current to loadNo. 2, 19 with Triac l3, and load No. l, 15 being deactivated. This isin view of the fact that the gate of Triac 13 is connected to AC powersource 11 through photocell 20. This photocell receives light inputsolely from lamp 30. When lamp 30 is not on, the photocell has a highresistance. This high resistance in the gate circuit of the Triac keepsthe Triac at cut-off.

Lamp 30, as to be explained further on in the specification, is actuatedto the on condition only when the system timer is in one of its timingcycles. The Triac 17 is actuated to the on condition by virtue of thelow resistance path between its gate and AC power source 11 provided byresistor 22 and load number 1,15.

The output of AC power source 11 is rectified and filtered by means ofDC power supply 35. The output of DC power supply 35 is connectedthrough lamp 30 to voltage regulator circuit 38 which forms part ofpower control circuit 40. The output of voltage regulator circuit 38 isfed to timer 42. Electronic switches 43 and 44 operate, as now to beexplained, in conjunction with touch plate 46 to control the operationof the timer and control circuits which respond thereto] To initiate atiming cycle, the operator momentarily touches the touchplate 46 withhis finger, this plate being a metallic plate which is connected in thegating circuit of electronic switch 43. Electronic switch 44 is normally(i.e. when timer 42 is not performing a timing cycle) activated andoperates in this condition to shunt out the output of voltage regulatorcircuit 38 so that no power is being delivered to timer 42.When'electronic switch 43 is activated by means of touch plate 46, itdrives electronic switch 44 to cut off thereby supplying power to timer42. When timer 42 is so energized it commences its timing cycle. Withthe shunt across voltage regulator circuit 38 removed so that current isbeing delivered to timer 42, lamp 30 is energized to in turn activatephotocell 20. This provides a low resistance path between the gate oftriac l3 and AC power source 11 to activate triac l3 and along with itload No. 1,15 which as already noted, may comprise the exposure lamp ofa photographic enlarger. With triac 13 activated, a shunt is appliedbetween the gate and the low side of triac l7 driving this triac to cutoff thereby deenergizingload No. 2, 19 which may comprise a safe light.7 When the timing operation of timer 42 has been completed, a signal isprovided from the timer to actuate electronic switch 44 to the oncondition" thereby restoring the shunt across voltage regulator circuit38 and interrupting the supply of current to the timer. This causes'thede-energization of lamp 30 which in turn effects the de-energization ofload No. 1, l5, and the energization of load No. 2, 19.

Referring now to FIG. 2, a schematic drawing of a preferred embodimentof the power control circuit 40 of the invention is illustrated. Thepower is supplied from DC power supply 35 through resistors 50 and 51 toseries connected Zener diodes 53-55. Connected in shunt across theseries connected Zener diodes is silicon controlled rectifier 44.'Thegate of silicon controlled rectifier 60 is connected through capacitor62 and resistor 63 to the negative terminal of DC power supply 35.Normally (i.e. except during the timing cycle of the timer), siliconcontrolled rectifier 60 is activiated by virtue of the forward biassupplied by the power supply and thus provides a shunt across the Zenerdiodes which connects the base of NPN transistor 70 to the negativeterminal of DC power supply 35. This maintains transistor 70 at cut offand thus interrupts the current path to the timer.

Silicon controlled rectifier 43 is also maintained at cut off in view ofthe fact that its gate, which is connected through capacitor 50 to touchplate 46, is effectively fioatingf atthis time. Capacitor 60 chargesthrough the path provided by resistors 67 and 68 and silicon controlledrectifier 44.Silicon controlled rectifier 43 is of a type having asensitive gate, (i.e., one that will trigger with less than microamps ofgate current); When the operator touches touch plate 46 this provides asufficient current to the gate of silicon controlled rectifier 43through capacitor 50 to activate the silicon control and rectifier,momentarily. The momentary activation of silicon controlled rectifier 43permits the discharge of capacitor 60 through resistor 67 and siliconcontrolled rectifier 43. This momentarily reverse biases siliconcontrolled rectifier 44 driving it to cut off. ln view of the fact thatresistor 68 is of a very high magnitude (of the order of 22 megohms) thesilicon controlled rectifier is current starved so that it immediatelyreturns to the deactivated state after its momentary actuation, its onlyfunction being to dump commutating capacitor 60. With silicon controlledrectifier 44 at cut off, the shunt is removed from across the zenerdiode network formed by Zener diodes 53-55 and a positive voltage isapplied to the base of transistor 70 to drive this transistor toconduction. This causes the activation from neon lamp 30 and provides acurrent path from the DC power supply to the timer.

When the timing cycle of the timer has been completed, a pulse 70 isgenerated by the timing circuit. This pulse is fed through capacitor 62to the gate of silicon controlled rectifier 44 to drive this siliconcontrolled rectifier back to the conductive state, thus interrupting thesupply of the current to the timer and deactivating neon lamp 30.Referring now to FIG. 3, a preferred embodiment of the timer utilized inthe device of the invention is schematically illustrated. The positivevoltage line from the power control circuit is connected to the drain offield effect transistor 77. The source of this transistor is connectedthrough potentiometer 79, resistor 80, capacitor 83, and resistor 84 tothe negative line 76 of the power control circuit. Transistor 77 acts asa linear current source for the resistive-capacitor charging circuitformed by resistors 79 and 84, potentiometer 80 and capacitor 83. A rampvoltage 87 is thus developed in the charging circuit. Potentiometer 79is used as a trimmer to adjust the charging current for optimumcharacteristics.

The ramp voltage 87 is fed through resistor 90 to the gate of fieldeffect transistor 92. The drain of this transistor is connected throughresistor to power line 75 while the source of this transistor isconnected to the anode of programmable unijunction transistor 97.Transistor 92 functions as a current amplifier and overcomes the offsetas is necessary to fire programmable unijunction transistor 97 withshort timing cycles. A fixed DC voltage is applied to the program gateof prog rammable unijunction transistor 97 from the arm of timingpotentiometer 100. This timing potentiometer is connected in a voltagedivider circuit formed by itself and resistors 102 and 103 which areconnected between lines 75 and 76. Timing potentiometer is preferably aprecision wire wound potentiometer and is calibrated so that it canbeset to provide the various desired timing outputs. When the ramp voltageoutput 102 of transistor 92 exceeds the voltage applied to the gate ofprogrammable unijunction transistor 97, the programmable unijunctiontransistor fires to produce an output pulse 70 at its cathode whichsignals the end of a timing cycle. This pulse as explained in connectionwith FIG. 2, is utilized as a keying signal which fires the powercontrol circuits to cut off the supply of power to the timer.

Field effect transistor is connected across capacitor 83 and operates todischarge this capacitor at the termination of each timing cycle. Duringthe timing cycle, transistor 110 is maintained at cut off by virtue ofthe negative bias applied to its gate. With the removal, however, of thepotential between lines 75 and 76, this bias disappears and an effectivedischarge path is provided for capacitor 83 through the transistor.

is intended .by way of illustration and example only, and

is not to be taken by way of limitation, the spirit and scope of thisinvention being limited only by the terms of the following claims.

l claim:

1. A timing control device for controlling the application of power froma power source through load means for predetermined periods of timecomprising:

a timer for generating a timing signal corresponding to the end of eachof said predetermined periods of time,

means for switching power from said power source to said load means, and

a power control circuit for controlling the application of power to saidtimer and actuating said means for switching power, the timing operationof said timer being initiated when power is supplied thereto from saidpower control circuit,

said timer including a resistive-capacitive charge circuit forgenerating a ramp voltage, a precision potentiometer connected to theoutput of said power control circuit to provide a selectable voltage andelectronic switch means having cathode and anode electrodes and acontrol gate, said control gate receiving the output 'of saidpotentiometer, one of said electrodes receiving said ramp voltage, thetiming signal appearing at the other of said electrodes when the rampvoltage goes above the voltage on said control gate,

said power control circuit receiving the output of said power source andincluding voltage regulator circuit means for regulating said powersource output and electronic switch means for effectively shunting saidregulator circuit at all times except during the timing cycles of saidtimer,

said power control circuit further including manually operable switchmeans for providing an actuating signal for said electronic switch meansto initiate the supply of current from said power control circuit tosaid timer, the timing signal from said timer being fed to saidelectronic switch means to actuate said electronic switch means toremove the supply of power to said timer'toterminate each-timing cycle.

2. The device of claim 1 wherein said electronic switch means comprisesa semiconductor switching device having a sensitive gate, said manuallyoperable switch means comprising a touch plate connected to the gate ofsaid switching device whereby the touching of said touch plate providescurrent to said said switching device.

3. The device of claim I wherein said load means comprises first andsecond loads and switch means responsive to said power control circuitfor alternatively activating one or the other of said loads.

4. The device of claim 1 wherein said voltage regulator circuit meanscomprises a plurality of series connected zener diodes, said electronicswitch means comprising a silicon controlled rectifier connected inshunt gate to fire across the series connected zener diodes.

5. The device of claim 1 wherein said means for switching power to saidload comprises an electronic switch having. a gate control circuit, aphotoelective cell in said gate control circuit, lamp means connected insaid power control circuit, said lamp means being driven to theilluminated state by said power control circuit to excite saidphotoelectric cell thereby causing said electronic switch to beactuated.

'6. The device of claim 1 and additionally including electronic switchmeans connected .across the capacitive portion of said charge circuitfor discharging said capacitive portion on the completion of each timingcycle, said switch means being activated in response to said timingsignal, and means for providing bias to said last mentioned switch meansto maintain said switch means in a deactivated state except whenactuated by said timing signal.

7. A timing control device for controlling the application of power froma power source to a load during predetermined time intervals comprising:

electronic switch means for interconnecting said power source and saidload, v

power control circuit means for controlling the operation of saidelectronic switch means, said power control circuit means includingmanually operable switch means, and

timer means for providing a timing control signal for controlling theoperation of said power control circuit means, said timer meansincluding a resistivecapacitive charge circuit for generating a rampvoltage, said charge circuit receiver a voltage from said power controlcircuit means to initiate the charging thereof in response to anactuation of said manually operable switch means, a potentiometerconnected to receive voltage from said power control circuit forselecting a desired voltage and a programmable unijunction transistor,the program gate of said unijunction transistor receiving the output ofsaid potentiometer, the anode of said unijunction transistor receivingsaid ramp voltage, said timing control signal appearing at the cathodeof said unijunction transistor when the ramp voltage at the anodethereof exceeds the voltage at the gate thereof.

8. The device of claim 7 wherein said manually operable switch meansincludes a silicon controlled rectifier having a sensitive gate and atouch plate for providing an actuation signal to said gate when touchedby an operator.

9. The device of claim 7 wherein said power control circuit meansincludes voltage regulator circuit means comprising a plurality ofseries connected zene'r diodes, a silicon controlled" rectifierconnected in shunt across said zener diodes, said silicon controlledrectifier being activated to effectively shunt out the current supply tosaid charge circuit and said potentiometer in response to said timingcontrol signal, said silicon controlled rectifier being deactivated inresponse to said manually operable switch means to remove said shunt andpermit the supply of current to said charge circuit and saidpotentiometer.

1. A timing control device for controlling the application of power froma power source through load means for predetermined periods of timecomprising: a timer for generating a timing signal cOrresponding to theend of each of said predetermined periods of time, means for switchingpower from said power source to said load means, and a power controlcircuit for controlling the application of power to said timer andactuating said means for switching power, the timing operation of saidtimer being initiated when power is supplied thereto from said powercontrol circuit, said timer including a resistive-capacitive chargecircuit for generating a ramp voltage, a precision potentiometerconnected to the output of said power control circuit to provide aselectable voltage and electronic switch means having cathode and anodeelectrodes and a control gate, said control gate receiving the output ofsaid potentiometer, one of said electrodes receiving said ramp voltage,the timing signal appearing at the other of said electrodes when theramp voltage goes above the voltage on said control gate, said powercontrol circuit receiving the output of said power source and includingvoltage regulator circuit means for regulating said power source outputand electronic switch means for effectively shunting said regulatorcircuit at all times except during the timing cycles of said timer, saidpower control circuit further including manually operable switch meansfor providing an actuating signal for said electronic switch means toinitiate the supply of current from said power control circuit to saidtimer, the timing signal from said timer being fed to said electronicswitch means to actuate said electronic switch means to remove thesupply of power to said timer to terminate each timing cycle.
 2. Thedevice of claim 1 wherein said electronic switch means comprises asemiconductor switching device having a sensitive gate, said manuallyoperable switch means comprising a touch plate connected to the gate ofsaid switching device whereby the touching of said touch plate providescurrent to said gate to fire said switching device.
 3. The device ofclaim 1 wherein said load means comprises first and second loads andswitch means responsive to said power control circuit for alternativelyactivating one or the other of said loads.
 4. The device of claim 1wherein said voltage regulator circuit means comprises a plurality ofseries connected zener diodes, said electronic switch means comprising asilicon controlled rectifier connected in shunt across the seriesconnected zener diodes.
 5. The device of claim 1 wherein said means forswitching power to said load comprises an electronic switch having agate control circuit, a photoelective cell in said gate control circuit,lamp means connected in said power control circuit, said lamp meansbeing driven to the illuminated state by said power control circuit toexcite said photoelectric cell thereby causing said electronic switch tobe actuated.
 6. The device of claim 1 and additionally includingelectronic switch means connected across the capacitive portion of saidcharge circuit for discharging said capacitive portion on the completionof each timing cycle, said switch means being activated in response tosaid timing signal, and means for providing bias to said last mentionedswitch means to maintain said switch means in a deactivated state exceptwhen actuated by said timing signal.
 7. A timing control device forcontrolling the application of power from a power source to a loadduring predetermined time intervals comprising: electronic switch meansfor interconnecting said power source and said load, power controlcircuit means for controlling the operation of said electronic switchmeans, said power control circuit means including manually operableswitch means, and timer means for providing a timing control signal forcontrolling the operation of said power control circuit means, saidtimer means including a resistive-capacitive charge circuit forgenerating a ramp voltage, said charge circuit receiver a voltage fromsaid power control circuit means to initiate the charging tHereof inresponse to an actuation of said manually operable switch means, apotentiometer connected to receive voltage from said power controlcircuit for selecting a desired voltage and a programmable unijunctiontransistor, the program gate of said unijunction transistor receivingthe output of said potentiometer, the anode of said unijunctiontransistor receiving said ramp voltage, said timing control signalappearing at the cathode of said unijunction transistor when the rampvoltage at the anode thereof exceeds the voltage at the gate thereof. 8.The device of claim 7 wherein said manually operable switch meansincludes a silicon controlled rectifier having a sensitive gate and atouch plate for providing an actuation signal to said gate when touchedby an operator.
 9. The device of claim 7 wherein said power controlcircuit means includes voltage regulator circuit means comprising aplurality of series connected zener diodes, a silicon controlledrectifier connected in shunt across said zener diodes, said siliconcontrolled rectifier being activated to effectively shunt out thecurrent supply to said charge circuit and said potentiometer in responseto said timing control signal, said silicon controlled rectifier beingdeactivated in response to said manually operable switch means to removesaid shunt and permit the supply of current to said charge circuit andsaid potentiometer.